It is widely known that an airbag is provided with a vent hole, through which gas inside the airbag is discharged when a vehicle occupant or the like bumps into the airbag in an inflated state, whereby the vehicle occupant or the like is softly received by the airbag.
Japanese Unexamined Patent Application Publication No. 6-127330 discloses an airbag in which a vent hole is closed before an occupant comes into contact with a near-occupant face of the airbag in an inflated state, but the vent hole opens when the occupant comes into contact with the near-occupant face of the inflated airbag and causes the near-occupant face to retract.
The foregoing publication describes that the vent hole is provided in an away-from-occupant face of the airbag, opposite the near-occupant face, and a slit is provided near the vent hole. A strap is made to pass through the slit. One end of the strap is routed in the inside of the airbag and is connected to the near-occupant face of the airbag. The other end of the strap is routed to pass through the slit and to extend along the outer surface of the airbag across the vent hole, and is connected to the outer surface of the airbag on a side across the vent hole from the slit.
According to the publication, when the airbag is inflated, the near-occupant face and the away-from-occupant face of the airbag move away from each other, causing the strap to be under tension. In this state, the other end of the strap is under tension along the outer surface of the airbag and overlies the vent hole, thereby closing the vent hole. Thus, the discharge of the gas through the vent hole is regulated, the pressure inside the airbag quickly increases, and the airbag is quickly deployed.
When the occupant comes into contact with the near-occupant face of the inflated airbag and causes the near-occupant face to retract inward of the airbag, the strap loosens and the other end of the strap moves away from the vent hole because of the gas pressure inside the airbag. Thus, the vent hole opens and the gas is discharged through the vent hole to the outside of the airbag. Consequently, the occupant is softly received by the airbag.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 6-127330
According to Japanese Unexamined Patent Application Publication No. 6-127330, if the airbag is inflated with a child seat placed on an occupant seat, the child seat comes into contact with a lower portion of the inflated airbag because the height of the child seat from the surface of the occupant seat is smaller than that of the upper half of the occupant's body. In such a case, since the near-occupant face of the airbag is not pushed inward of the airbag, the vent hole does not open.
An embodiment is disclosed in which a sensor or the like that checks whether an occupant is seated on the occupant seat or a child seat is placed on the occupant seat is provided. If it is determined that a child seat is placed on the occupant seat, an inflator is not operated. However, such an embodiment increases the cost of configuring an airbag device.